The purposed work will investigate the transducing properties of slowly adapting stretch receptors of the trachea in relation with the mechanical properties of their environment: The trachea as a whole and its membranous posterior wall which has been proved to be the unique site of these receptors. The mechanical coupling between the semi-rigid tracheal cartilages and the membranous posterior wall will be considered as a means of providing the capability of these receptors to sensing both negative and positive transmural pressure. The reflex influences originating from the extrathoracic portion of the trachea will be studied considering the distinct situation of this segment of the airways during the breathing cycle. The changes in transmural pressure here are out of phase with those in the intrathoracic airways and likewise, the activation of the corresponding stretch receptors. Therefore, even if the central connection of these receptors were the same, their reflex influences might be different. The precise location of fast adapting "irritant" receptors in the larger airways will be further investigated either through bronchoscopy or directly in the open extrathoracic portion of the trachea.